Purpose The purpose of this paper is twofold: first, to observe an influence of different Composite Fibre-Reinforced Polymer (CFRP) patches, whose application to metals is very easy, in suppling and significantly elongating the service time; and second, the numerical calculation of the reduced stress intensity factor (SIF) range for strengthened cracked steel specimens. Design/methodology/approach One of the successful strengthening methods is the CFRP patching along the fatigue crack paths. The presented approach has been studied and discussed in this paper on the background of the numerical and experimental data. As it was expected, the proposed strengthening method is efficient and promising in case of the “immediate” repairs of critical members with cracks. The manufacturing process of specimens and test methodology as well as numerical approach to calculate SIFs for various reinforcements of steel specimens are presented. For this purpose, the Extended Finite Element Method was involved and described. Findings The main mechanism of fatigue crack growth retardation is associated with local ΔK reduction due to CFRP patches; any type of reinforcement results in an increase in af and a significant decrease in SIF values. The beach-marking method is described as a good, reliable and comprehensive method to capture the crack propagation in structures consisting of various materials and could be applied successfully for mixed mode testing. Originality/value A detailed experimental-numerical approach for fatigue crack growth in long-term operated structures made of steel is presented. The strengthening methodology is presented with consideration of the various CFRP patches configurations.
Current elevators are mostly designed as rope-dependent elevators. Main components in the roping system are the deflection sheaves which are conventional manufactured of grey cast iron. Due to the high weight of cast iron sheaves there is a high potential for reducing mass, especially when regarding aspects of effort, safety and ergonomics while assembly and maintenance in the elevator shaft. Within the framework of a R&D co-operation the Chemnitz University of Technology and the AMB Oberlungwitz GmbH developed a fibre-reinforced plastic sheave that comply with the requirements of lightweight design. The technological basic approach to realize that development is compression molding of glass-mat-reinforced thermoplastics (GMT). The project includes the whole development-chain, consisting of part design, tool design, process chain arrangement, parameter studies as well as validation of specimen. In the course of the project appeared a high potential for improvement of the part properties by alternative design solutions. In this context current activities are focused on multi material design methods such as combining GMT with other thermoplastic prepregs. In this manner it is possible to equip every local area with the specific properties that are required. For example the ribs of the sheave, that receive highest values of stress, can be made of materials with continuous-fibre-reinforcement while the basic part body consists of GMT, which is long-fibre-reinforced. This method also enables to avoid process influenced effects like the segregation of the fibre-matrix distribution in GMT. Additionally the input of different materials offers chances to inlay non-preheated prepreg blanks into the compression mould, so that the amount of the preheated material volume can be reduced. In this way cycle times and also lost of temperature due to transfer times of the heated blanks to the mould can be reduced.
Purpose The purpose of this paper is to present a case of fatigue damaging of the attacking roller of the WRC class car. Fatigue fractures are a very essential source of cognitive and usable information about the cause of damage of various engineering components. Microfractography allows extending considerations about the main mechanism of initiation and growth of fatigue cracks. The presented research procedure allowed establishing the root cause analysis of the premature fatigue failure of the pinion shaft. Design/methodology/approach The specimen for metallographic investigation was extracted from failures pinion shaft. According to the light microscopy and scanning electron microscopy (SEM) study, the detailed observations of microstructure were performed. Fracture surface of pinion shaft and teeth were examined using SEM. The presence of the extraordinary mechanical notch was found as a potential failure root cause. Findings The potential cause of premature failure pinion shaft assembly has been found. The microstructural causes were excluded due to correctly performed heat treatment. The main reason of failure was improper mechanical machining of the pinion shaft due to large mechanical notch. Originality/value A detailed metallographic expertise route is presented. The usefulness of fractographic analysis is confirmed in case of the failure analysis of premature pinion shaft. The root cause was found and the concluding remarks are included in this paper.
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